I'm a bro-scientist on this subject, and often suggest others supplement with Vit D because, "it probably won’t hurt, and it might help".
While I have generally suggested people take somewhere between 1,000 IU - 4,000 IU daily, I do always suggest people test their blood levels if taking doses in this range because toxicity can very occasionally occur if you're taking doses above 2,000 IU daily. Anything above 5,000 IUs daily and you're almost certainly taking too much.
I think it's worth remembering that in the Northern hemisphere a significant percentage of people have Vit D deficiencies in the winter and about 50% of people have insufficient Vitamin D levels.
Long-term having insufficient Vitamin D levels can increase your risk of cancer, heart disease and various other chronic diseases.
Given we're just coming out of winter in the Northern Hemisphere, if you're not currently supplementing Vit D and you're reading this comment from somewhere in the Northern Hemisphere there's a greater than 50% chance you currently have insufficient levels of Vit D.
Here in the UK the NHS warns against taking more than 4,000 IU of Vit D daily if you're an adult, and generally doses of 1,000 IU - 2,000 IUs are suggested to maintain adequate Vit D levels. I think these are on the high end if I'm honest, but the fact the NHS says this would suggests that 4,000 IUs daily in adults is probably generally tolerable which roughly correlates with the research and personal experimentation I've done on this subject.
Supplementing with 2,000 IU daily is almost never going to cause problems in an adult. Personally I supplement with 4,000 IUs daily in the winter and generally drop this to 2,000 IUs in summer, and I know from testing this keeps my Vit D levels slightly above the recommended 50 ng/mL all year round (although imo 70 ng/ml is a better target). I will note though that I get very little sun exposure so what I take is probably on the higher end of what's needed to maintain healthy levels of Vit D.
I'll also note that typically toxicity won't occur in most people until they reach levels greater than 150ng/ml and I get no where near this despite taking a rather high daily dose for years.
What I'm trying to say here is that evidence does suggest that most people probably should be supplementing with Vit D and not doing so for fear of Vit D toxicity is kinda stupid because unless you're taking ridiculous doses for months on end you're realistically never going to reach toxicity levels.
If you're really worried about Vit D toxicity and do not want to do blood testing, please consider just supplementing with 500 - 1,000 IU / daily. Your risk of toxicity at these levels is probably non-existent, but it should ensure at the very least you never become deficient. In my opinion there's really no good reason not to do this, especially if you're at increased risk of having low Vit D (such as being elderly or having a darker skin ton).
Vit D deficiency is such a big problem though that I think it's crazy we don't do more to encourage more people to supplement with it to be honest.